The present invention relates to a method of processing an optical fiber employed in an optical communication apparatus.
An optical communication apparatus includes optical components such as a laser diode (LD), a lens that converges light from the LD, and an optical fiber, for transmitting light emitted by the LD and modulated according to information, to the optical fiber. An optical communication module that serves as an ONU (Optical Network Unit), through which the optical fiber communication is introduced into a subscriber's house, further includes a photoreceptor and a WDM (Wavelength Division Multiplex) filter that separates light of different wavelengths, for performing interactive communication in which a single optical fiber is used for both transmission and reception in common.
In such an optical communication module, signal light from the LD has to be introduced to a generally central portion of a core of the optical fiber, so as to transmit or receive the signal light through the optical fiber. In other words, the LD has to be precisely positioned with respect to the core of only a few microns in diameter, of the optical fiber. In a conventional positioning method, an amount of light emitted from the LD is detected, and the light from the LD is decided to be incident upon a generally central portion of the core if the light amount satisfies a predetermined level. Normally, those optical components are firmly fixed by welding or with an adhesive, after the positioning process.
According to the conventional positioning method, however, it is impossible to decide how much and in which direction the incident position of the light from the LD is shifted, when the amount of the emitted light is below the predetermined level. Accordingly, the relative positioning between the incident position and the core of the optical fiber has to be repeated on a “trial and error” basis, until the amount of the light emitted by the LD reaches the predetermined level, which is troublesome and time consuming.
Further, though the relative positions of the components are fixed with an adhesive upon completing the positioning operation by the above method, to thereby constitute an optical communication module, the following issues still remain unsettled. Firstly, when the optical communication module is fabricated as above, the evaluation of the product cannot be executed until the adhesive completely dries after the adhesion, since deformation of or damage to the components due to shrinkage of the adhesive or the process may occur. It is therefore difficult to achieve a high yield with such an optical communication module. Secondly, if the performance level of the optical communication module deteriorates with time, it is no longer possible to readjust the performance, and hence the high-precision positioning performance cannot be maintained.
Desirable remedies for solving the foregoing problems include actually detecting the incident position of the light from the LD on a light receiving facet of the optical fiber, so as to adjust the position such that the incident position coincides with the center of the core, and constituting the optical communication module so as to constantly perform the positioning operation with respect to the light from the LD. In order to practically carry out such remedies, the light receiving facet of the optical fiber has to be processed so as to enable detecting the incident position on the light receiving facet with high precision, and processing the light receiving facet so that the boundary between the core and the clad can be clearly identified on the light receiving facet of the optical fiber.
An example of processing a light receiving facet of an optical fiber is disclosed in each of Japanese Patent Provisional Publications No. H05-107428 (hereafter, referred to as a document 1) and No. 2001-305382 (hereafter, referred to as a document 2).
The documents 1 and 2 both aim at improvement in propagation efficiency of light when optically connecting an optical fiber with another optical device such as an optical waveguide. These documents disclose a method of forming a core facet of the optical fiber in a protruding shape, or providing a protruding member close to the core facet. The method of processing disclosed in the documents 1 and 2 can be appropriately employed when processing an emitting facet situated opposite to another optical device, i.e. a facet serving for optical connection with another optical device.
The method of forming the core facet in a protruding shape according to the document 1 utilizes a difference in etching rate due to a difference in composition between the core and the clad, and is hence unable to precisely process the core facet so that the core can be clearly distinguished from the clad. Accordingly, employing an optical fiber processed as above does not lead to high-precision detection of an incident position of light from the LD.
In the method of forming a protruding member close to the core according to the document 2, it is difficult to achieve a correct alignment between the optical fiber and a mask used for exposing only a predetermined portion of the optical fiber. Therefore, the method disclosed in the document 2 is unable to precisely process the core facet so that the core can be clearly distinguished from the clad. Consequently, the method of processing disclosed in the documents 1 and 2 cannot be employed as a method of processing a light receiving facet intended for the high-precision position detection and positioning operation for the light receiving facet.